The competitive renewal of our program project grant application is submitted by investigators who propose to continue their studies on the unique properties of human milk. All projects address the biologic consequences through protocols which utilize in vitro assays, animal models, and humans. The projects generally seek to define and characterize factors in human milk that protect newborn infants from disease. Certain consequences of the luminal milk gastrointestinal tract interactions that pertain to protection of the infant will continue to be examined. Animal models will be utilized with study of human subjects is not possible, but human infants will be studied whenever appropriate. The respective projects and subcontracts will consider: 1) the role of soluble milk factors in the prevention of shigellosis; 2) the anti-inflammatory characteristics of human milk; 3) the role of the secretory immune system in viral enteric pathogen infection; 4) isolation, characterization and testing of the protective factor(s) in human milk against heat-stable enterotoxin of E. coli; and 5) the role of human milk in the prevention of Campylobacter infection. Each of the projects will be supported by epidemiology/statistical, biochemical, and molecular biology core sections.